Compressed cathode support structure



RM H mm M V T n w y i a m P. L. SPENCER COMPRESSED CATHODE SUPPORT STRUCTURE- Filed May 19, 1948 Sept. 26, 1950 Patented Sept. 26, 1950 "U N IT ED STATES PATENT QFFICE 2,524,061 COMPRESSED oA'rIioDE siiri oii'r STRUCTURE Percy L. Spencer, West Newton, Mass, assignoi .to Raytheon Manufacturing Company, Newton,

Mass, a corporation of Delaware Application May, 19, 1948, Serial No. 27,931

.91Glaims. (Cl.. 2.50-+27.5)

be formed by molding, as described in the aforesaid Hanson application. Y I

Solid cathode sleeves of the aforementioned type have-been found, however, to be of arather ragile nature, such that they will not withstand, to a very great degree, s-uddenchanges in temperature, but instead will very often crack or break in a rather short time when subjected to such temperature changes, In other words, such sleeves are sensitive or responsive to heat shock.

In many cases, it is desirable to utilize for magnetrons a cathode of-the indirectly-heated type. If it is attemped to utilize asolid cathode sleeve of" the aforesaid rather fragile type in a conventional indirectly-heated structure, serious difi'iculties arise, due to the fragile nature and extreme sensitivity to heat shock of such a sleeve.

It has been found, according to this invention, that if such a powdered sleeve is supported only at its ends and a heater is positioned therein, in

the conventional manner, the cathode is still rathershort-lived, due to the fragility of the sleeve or to the limited area, and therefore the relative weakness, of the joint between the sleeve and the support.

Accordingly, an object of this invention is to devise an indirectly-heated cathode structure utilizing a moldedlpowdered sleeve, in whichthe above-described difiiculties are overcome.

Another object is to devise ahmeansfor using a solid cathodesleeveofa fragile type, in an indirectly-heated cathode structure, in .an effective and efficient manner, such that the structure has a long usable life.

A furtherobject is to provide, a cathode structure wherein a fragile cathode sleeve is supported in a rigid manner throughout its length, and yet in which the support permits substantially unimpeded expansionmand contraction of the said sleeve.

A still further objectis -to.devise. a cathode structure formagnetrons, the emissiveportion of which operates at a rather elevated itemperature, and yet in which the portions of the supports beyond the ends of the said emissiveportion remain cool, relative to the temperature of said emissive portion.

The foregoing and other objects of the invention will bebest understood from the following description of an exemplification thereof, reference being had to the accompanying drawing, wherein:

Fig-l is an elevation'of a cathode sleeve of th type utilized in this invention;

Fig. 2 is a 'vertical section through a cathode structure according to this invention, certain parts thereof being shown in elevation;

.Fig. 3 is an elevation of the upper portion of I thestructure of Fig. 2, on an enlarged scale;

Fig. 4 is a horizontal sectiontaken online --44 of Fig. 2, looking in the direction of the arrows; and

Fig.5 is a horizontal section taken on line 55 of Fig 2,-kll 1g in the direction ofthe arrows.

Referring now to the drawing, reference numeral lflindicates a cylindrical sleeve of compressed, intimately admixed, powdered thoria (thorium oxide) and a powdered refractory metal,

metal compound, metal alloy, or mixture of metals, such as molybdenum, molybdenum carbide, -molybdenum-cobalt, molybdenum-nickel,

tungsten, tungsten carbide, tungsten cobalt, or tungsten-nickel. Such' sleeves are described and claimed per se in the above-identified copending patents of Hanson and Spencer, and may be fabricated as disclosed in the aforesaid Hanson application. Sleeve it, when heated'to atemperature of thermionic emission, emits electrons copiously, and is particularly suitable for use as an emitter in electron discharge devices of th magnetron type. r

In order to position and rigidly support sleeve ill, said sleeve is slipped over a thin cylindrical metallic-supporting sleeve H which is made of a material capable of withstanding high temperatures, such as molybdenum for example. The cathode sleeve I0 is rigidly secured, as by brazing with platinum or with molybdenum powder, to the outer surface of the central portion of supporting sleeve H. Sleeve It has a length substantially in excess of that of sleeve It, and the former is provided with a plurality, here shown as eight, of equally-spaced parallel longitudinally-extendin slots l2, which have a length somewhat greater than the length of cathode sleeve. I0 and which are .locatedin the central rate metal strips between adjacent slots portion of sleeve II which is covered by sleeve ID in the assembled structure. At both its upper and lower ends, each slot I2 communicates with a corresponding transversely-extending slot I3, 50 that each of the combined slots I2-I3 is in the shape of the letter I. The cener lines of all of the upper transverse slots l3 lie in a common horizontal plane, as do also the center lines of all of the lower transverse slots I3, and the lengths of all of the said slots I3 are made such as to leave only narrow areas of metal between adjacent slots, as shown. Supporting member II, with the slots I2I3 therein, is preferably formed by being stamped out of sheet material and afterwards being bent into cylindrical shape, as indicated by the longitudinal seam I4 indicated on the drawings. 7

Slots I2 extend throughout the length of the area of attachment of cathode sleeve II! to supporting sleeve II, sleeve It being secured rigidly to sleeve II in said area of attachment. Slots I2 extend entirely through the thickness of sleeve II and are spaced from each other, leaving sepa- I2. Such slots provide a certain resilience for the central portion of supporting sleeve II, to which portion cathode sleeve I is secured, such as to allow for differential expansion between the material of sleeve I0 and th material of sleeve II. By such structure, the cathode sleeve Ill can expand and contract freely in response to temperature changes without strains being produced therein, while at the same time said cathode sleeve is rigidly attached and supported by sleeve II at all times, since such differential expansion between sleeves I0 and I I is provided for by slots I2- Undue strains in sleeve I0 are thus prevented, and at the same time the joint between sleeves I9 and II is substantially unaffected by temperature changes, thus increasing the life of the cathode.

The cathode sleeve I0 is heated to the temperature of thermionic emission by th means to be hereinafter described, which temperature is rather high, and it is desirable, for many reasons, to prevent the end portions of supporting member II from being heated to this high temperature. The transverse slots l3, at each end of the central portion of sleeve or member II, provide a heat choke, heat shield, or heat interrupter to minimize the conduction of heat from the heated central portion of sleeve II, to the end portions of said sleeve. Thus, as shown in Fig. 4, there are only very narrow metallic areas between adjacent slots I3, the greater part of the horizontal cross-section through slots I3 being insulating air space. Since the cross-section of heat-conducting metal between the end and central portions of supporting sleeve II is in this way held to an absolute minimum, the conduction of heat from the central to the end portions of said sleeve is limited to a very small amount, so that said end portions remain cool relative to said central portion, when said central portion is heated for electron emission.

A hollow cylindrical metallic sleeve I is fastened, as by welding or brazing, to the lower end of supporting sleeve II, the upper end of sleeve I5 being provided with aninternal shoulder on which rests the lower end of sleeve I I. Sleeve I5 is made of a metal, such as Kovar, which is commonly used for sealing to glass, and a hollow glass insulating bead I6 is fused at its upper end to the lower end of sleeve I5. The lower end of bead I6 is in turn fused to the upper end of a second metallic sleeve I! which is also preferably made of Kovar. In order to secure the lower end of an elongated rigid supporting conductor I8 centrally or axially of members II, I5, l5 and ll, a dished metallic member I5, having an apertur in its center through which conductor I8 passes and in which said conductor is secured, is fastened at its outer edge, as by welding or brazing, to the lower end of member I'I. Thus, conductor I8 is mounted centrally of sleeves II and I5 and is insulated therefrom by bead IS.

A heater wire 20, of tungsten or other suitable material, fashioned in the form of a helix, has its lower end rigidly secured centrally of sleeve I I to the upper end of conductor I8, which upper end is located a little above the lower end of sleeve II. Heater 20 therefore is mounted centrally inside supporting sleeve II, and the coils thereof extend somewhat beyond the upper and lower end surfaces of cathode sleeve II]. In order to secure the upper end of heater 20 in position, an imperforate metallic cap or cover 2 I, having a central outwardly-extending projection ZIa thereon, is secured to the upper end of sleeve II in any suitable manner. The upper end of heater wire 28 is bent toward the center of the coil thereof, as shown, and is welded to the inside or lower surface of projection 2 Ia, this projection being provided for easy and convenient welding. In this way, by rigid attachment to conductor I8 and to cover member 2I, heater 20 is held in position centrally of sleeve II.

A lead wire 22 is electrically connected to sleeve I5, and another lead wire 23 is electrically connected to conductor I8. When a suitable source of heater voltage, here represented by a battery 24, is connected between leads 22 and 23, current flows through lead 23, conductor I8, heater 20, cap 2I, sleeve II, sleeve I5, and lead 22, the current passing through heater 20 being converted to heat therein which heats cathode sleeve I0 to the temperature of thermionic emission. Due to the high resistance of sleeve IE, only a very small amount of heating current will flow through said sleeve.

This completes the description of the aforesaid exemplification of the present invention. It will be noted that there has been provided an effective and easily-fabricated cathode structure having a longer life than generally available prior to this invention, and one which is suitable for use in high-power continuous-wave magnetrons.

Of course, it is to be understood that this invention is not limited to the particular details as described above, as many equivalents will suggest themselves to those skilled in the art. It is accordingly desired that the appended claims be given a broad interpretation commensurate with the scope of this invention within the art.

What is claimed is:

1. A cathode structure comprising a supporting 3. A cathode structure comprising an elongated metallic supporting sleeve, a com-pressed sleeve of powdered electron-emissive material surrounding and secured to the central portion of said supporting sleeve, said supporting sleeve being provided with openings for inhibiting the flow of heat from said central portion to the two end portions thereof, and means positioned inside said supporting sleeve for heating the central portion thereof and thereby also said compressed sleeve.

4. A cathode structure comprising a thinwalled supporting sleeve of molybdenum, a compressed sleeve of powdered thoria and molybdenum surrounding and secured to said supporting sleeve, and heater means positioned inside said supporting sleeve.

5. A cathode structure comprising an elongated metallic supporting sleeve, a compressed sleeve of powdered electron-emissive material surrounding and-secured to the central portion of said supporting sleeve, said supporting sleeve being provided with openings for inhibiting the flow of heat from said central portion to the two end portions thereof and being further provided with slots permitting difierential expansion of said two sleeves, and means positioned inside said supporting sleeve for heating the central portion thereof and thereby also said compressed sleeve.

6. A cathode structure comprising an elongated metallic supporting sleeve, a compressed sleeve of powdered electron-emissive material surroundmg and secured to the central portion of said supporting sleeve, said supporting sleeve being provided with a plurality of longitudinally-extending slots in the central portion thereof for permitting differential expansion of said twosleeves, and

heater means positioned inside said supporting I 8. A cathode structure comprising an elongated 1 thin-walled supporting sleeve of molybdenum, a

compressed sleeve of p0Wdered thoria and molybdenum surrounding and secured to the central portion of said supporting sleeve, said supporting sleeve being provided with slots permitting difierential expansion of said two sleeves and being further provided with means for inhibiting the flow of heat from said central portion to the two end portions thereof, and means positioned inside said supporting sleeve for heating the central portion thereof and thereby also said compressed sleeve.

9. A cathode structure comprising a metallic supporting sleeve, a compressed sleeve of'powdered electrcn-emissive material surrounding and secured to said supporting sleeve, said supporting sleeve being provided with slots in the portion of said metallic sleeve surrounded by said compressed sleeve thereby permitting differential expansion of said two sleeves, a stiff supporting conductor mounted substantially axiall of said supporting sleeve and insulated therefrom, and a coiled heater mounted substantially concentrically of said supporting sleeve, said heater having one end secured and electrically connected to said conductor and its opposite end secured and electrically connected to said supporting sleeve.

PERCY L. SPENCER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Great Britain June3, 1926 

